DNA replication occurs in S phase. The entry of cells into S phase is regulated by the tumor suppressor protein Rb. The statements below are made with reference to the role of Rb.
A. Rb binds to E2F in the cytosol and prevents E2F entry into the nucleus.
B. Rb is phosphorylated by cyclin A/cdk 4.
C. Phospho-Rb activates E2F.
D. E2F activates cyclin E production which promotes the G1/S transition.

Which one of the following options represents all correct statements?

Correct option is D

Explanation-

Statement A -  Rb binds to E2F in the cytosol and prevents E2F entry into the nucleus  -  INCORRECT
Rb does bind to E2F, but this interaction happens inside the nucleus, not in the cytosol. So, this statement is factually incorrect.
Statement B -  Rb is phosphorylated by cyclin A/CDK4  - INCORRECT
This is a misstatement. Cyclin A partners with CDK2, not CDK4. Rb is actually phosphorylated by cyclin D/CDK4/6 in early G1 phase. So this is also not correct.
Statement C - Phospho-Rb activates E2F   -  CORRECT
Once Rb is phosphorylated, it releases E2F, allowing E2F to activate transcription of genes for S phase entry. So, this statement is accurate.
Statement D - E2F activates cyclin E production which promotes the G1/S transition   - CORRECT
Free E2F indeed activates cyclin E gene transcription, which is critical for the G1 to S phase transition. So, this statement is fully correct.

Final Answer:
Only C and D are correct
Therefore, Option d (C and D only) is the correct answer.